3 Chapter 6 Residential and commercial buildings EXECUTIVE SUMMARY In 2004, emissions from the buildings sector including through electricity use were about 8.6 GtCO 2, 0.1 GtCO 2 - eq N 2 O, 0.4 GtCO 2 -eq CH 4 and 1.5 GtCO 2 -eq halocarbons (including CFCs and HCFCs). Using an accounting system that attributes CO 2 emissions to electricity supply rather than buildings end-uses, the direct energy-related carbon dioxide emissions of the building sector are about 3 Gt/yr. For the buildings sector the literature uses a variety of baselines. Therefore a baseline was derived for this sector based on the literature, resulting in emissions between the B2 and A1B SRES scenarios, with 11.1 Gt of emissions of CO 2 in 2020 and 14.3 GtCO 2 in 2030 (including electricity emissions but omitting halocarbons, which could conceivably be substantially phased out by 2030). Measures to reduce greenhouse gas (GHG) emissions from buildings fall into one of three categories: reducing energy consumption and embodied energy in buildings, switching to low-carbon fuels including a higher share of renewable energy, or controlling the emissions of non-co 2 GHG gases. 2 This chapter devotes most attention to improving energy efficiency in new and existing buildings, which encompasses the most diverse, largest and most cost-effective mitigation opportunities in buildings. The key conclusion of the chapter is that substantial reductions in CO 2 emissions from energy use in buildings can be achieved over the coming years using mature technologies for energy efficiency that already exist widely and that have been successfully used (high agreement, much evidence). A significant portion of these savings can be achieved in ways that reduce life-cycle costs, thus providing reductions in CO 2 emissions that have a net benefit rather than cost. However, due to the long lifetime of buildings and their equipment, as well as the strong and numerous market barriers prevailing in this sector, many buildings do not apply these basic technologies to the level life-cycle cost minimisation would warrant (high agreement, much evidence). Our survey of the literature (80 studies) indicates that there is a global potential to reduce approximately 29% of the projected baseline emissions by 2020 cost-effectively in the residential and commercial sectors, the highest among all sectors studied in this report (high agreement, much evidence). Additionally at least 3% of baseline emissions can be avoided at costs up to 20 US$/tCO 2 and 4% more if costs up to 100 US$/tCO 2 are considered. However, due to the large opportunities at lowcosts, the high-cost potential has been assessed to a limited extent, and thus this figure is an underestimate (high agreement, much evidence). Using the global baseline CO 2 emission projections for buildings, these estimates represent a reduction of approximately 3.2, 3.6 and 4.0 GtCO 2 /yr in 2020, at zero, 20 US$/tCO 2 and 100 US$/tCO 2 respectively. Our extrapolation of the potentials to the year 2030 suggests that, globally, about 4.5, 5.0 and 5.6 GtCO 2 at negative cost, <20 US$ and <100 US$/tCO 2 -eq respectively, can be reduced (approximately 30, 35 and 40% of the projected baseline emissions) (medium agreement, limited evidence). These numbers are associated with significantly lower levels of certainty than the 2020 ones due to very limited research available for While occupant behaviour, culture and consumer choice and use of technologies are also major determinants of energy use in buildings and play a fundamental role in determining CO 2 emissions (high agreement, limited evidence), the potential reduction through non-technological options is rarely assessed and the potential leverage of policies over these is poorly understood. Due to the limited number of demand-side enduse efficiency options considered by the studies, the omission of non-technological options and the often significant cobenefits, as well as the exclusion of advanced integrated highly efficiency buildings, the real potential is likely to be higher (high agreement, limited evidence). There is a broad array of accessible and cost-effective technologies and know-how that have not as yet been widely adopted, which can abate GHG emissions in buildings to a significant extent. These include passive solar design, highefficiency lighting and appliances 3, highly efficient ventilation and cooling systems, solar water heaters, insulation materials and techniques, high-reflectivity building materials and multiple glazing. The largest savings in energy use (75% or higher) occur for new buildings, through designing and operating buildings as complete systems. Realizing these savings requires an integrated design process involving architects, engineers, contractors and clients, with full consideration of opportunities for passively reducing building energy demands. Over the whole building stock the largest portion of carbon savings by 2030 is in retrofitting existing buildings and replacing energyusing equipment due to the slow turnover of the stock (high agreement, much evidence). Implementing carbon mitigation options in buildings is associated with a wide range of co-benefits. While financial assessment has been limited, it is estimated that their overall value may be higher than those of the energy savings benefits (medium agreement, limited evidence). Economic co-benefits include the creation of jobs and business opportunities, increased economic competitiveness and energy security. Other co-benefits include social welfare benefits for low-income households, increased access to energy services, improved indoor and outdoor air quality, as well as increased comfort, 2 Fuel switching is largely the province of Chapter 4, energy supply. 3 By appliances, we mean all electricity-using devices, with the exception of equipment used for heating, cooling and lighting. 389

4 Residential and commercial buildings Chapter 6 health and quality of life. In developing countries, safe and highefficiency cooking devices and high-efficiency electric lighting would not only abate substantial GHG emissions, but would reduce mortality and morbidity due to indoor air pollution by millions of cases worldwide annually (high agreement, medium evidence). There are, however, substantial market barriers that need to be overcome and a faster pace of well-enforced policies and programmes pursued for energy efficiency and de-carbonisation to achieve the indicated high negative and low-cost mitigation potential. These barriers include high costs of gathering reliable information on energy efficiency measures, lack of proper incentives (e.g., between landlords who would pay for efficiency and tenants who realize the benefits), limitations in access to financing, subsidies on energy prices, as well as the fragmentation of the building industry and the design process into many professions, trades, work stages and industries. These barriers are especially strong and diverse in the residential and commercial sectors; therefore, overcoming them is only possible through a diverse portfolio of policy instruments (high agreement, medium evidence). Energy efficiency and utilisation of renewable energy in buildings offer a large portfolio of options where synergies between sustainable development and GHG abatement exist. The most relevant of these for the least developed countries are safe and efficient cooking stoves that, while cutting GHG emissions, significantly, reduce mortality and morbidity by reducing indoor air pollution. Such devices also reduce the workload for women and children and decrease the demands placed on scarce natural resources. Reduced energy payments resulting from energy-efficiency and utilisation of buildinglevel renewable energy resources improve social welfare and enhance access to energy services. A variety of government policies have been demonstrated to be successful in many countries in reducing energy-related CO 2 emissions in buildings (high agreement, much evidence). Among these are continuously updated appliance standards and building energy codes and labelling, energy pricing measures and financial incentives, utility demand-side management programmes, public sector energy leadership programmes including procurement policies, education and training initiatives and the promotion of energy service companies. The greatest challenge is the development of effective strategies for retrofitting existing buildings due to their slow turnover. Since climate change literacy, awareness of technological, cultural and behavioural choices are important preconditions to fully operating policies, applying these policy approaches needs to go hand in hand with programmes that increase consumer access to information and awareness and knowledge through education. To sum up, while buildings offer the largest share of costeffective opportunities for GHG mitigation among the sectors examined in this report, achieving a lower carbon future will require very significant efforts to enhance programmes and policies for energy efficiency in buildings and low-carbon energy sources well beyond what is happening today. 390

5 Chapter 6 Residential and commercial buildings 6.1 Introduction Measures to reduce greenhouse gas (GHG) emissions from buildings fall into one of three categories: reducing energy consumption 4 and embodied energy in buildings, switching to low-carbon fuels including a higher share of renewable energy, or controlling the emissions of non-co 2 GHG gases. Renewable and low-carbon energy can be supplied to buildings or generated on-site by distributed generation technologies. Steps to decarbonise electricity generation can eliminate a substantial share of present emissions in buildings. Chapter 4 describes the options for centralized renewable energy generation, while this chapter covers building-level options for low-carbon electricity generation on-site. This chapter devotes most attention to energy efficiency in new and existing buildings, as fuel switching is largely covered elsewhere in this report (Chapter 4). Non- CO 2 GHGs are treated in depth in the IPCC special report on safeguarding the ozone layer and the climate system (IPCC/ TEAP, 2005), but some of the most significant issues related to buildings are discussed in this chapter as well. A very large number of technologies that are commercially available and tested in practice can substantially reduce energy use while providing the same services and often substantial co-benefits. After a review of recent trends in building energy use followed by a description of scenarios of energy use and associated GHG emissions, this chapter provides an overview of the various possibilities in buildings to reduce GHG emissions. Next, a selection of these technologies and practices is illustrated by a few examples, demonstrating the plethora of opportunities to achieve GHG emission reductions as significant as 70 80%. This is followed by a discussion of co-benefits from reducing GHG emissions from buildings, and a review of studies that have estimated the magnitude and costs of potential GHG reductions worldwide. In spite of the availability of these high-efficiency technologies and practices, energy use in buildings continues to be much higher than necessary. There are many reasons for this energy waste in buildings. The chapter continues with identifying the key barriers that prevent rational decision-making in energy-related choices affecting energy use in buildings. Countries throughout the world have applied a variety of policies in order to deal with these market imperfections. The following sections offer an insight into the experiences with the various policy instruments applied in buildings to cut GHG emissions worldwide. The past five years have shown increasing application of these policies in many countries in Europe and growing interest in several key developing and transition economies. In spite of this fact, global CO 2 emissions resulting from energy use in buildings have increased at an average of 2.7% per year in the past five years for which data is available ( ). The substantial barriers that need to be overcome and the relatively slow pace of policies and programmes for energy efficiency will provide major challenges to rapid achievement of low-emission buildings. 6.2 Trends in buildings sector emissions In 2004, direct emissions from the buildings sector (excluding the emissions from electricity use) were about 3 GtCO 2, 0.4 GtCO 2 -eq CH 4, 0.1 GtCO 2 -eq N 2 O and 1.5 GtCO 2 - eq halocarbons (including CFCs and HCFCs). As mitigation in this sector includes a lot of measures aimed at electricity saving it is useful to compare the mitigation potential with carbon dioxide emissions, including those through the use of electricity. When including the emissions from electricity use, energy-related carbon dioxide emissions were 8.6 Gt/yr (Price et al., 2006), or almost a quarter of the global total carbon dioxide emissions as reported in Chapter 1. IEA estimates a somewhat higher fraction of carbon dioxide emissions due to buildings. Figure 6.1 shows the estimated emissions of CO 2 from energy use in buildings from two different perspectives. The bar at the left represents emissions of CO 2 from all energy end-uses in buildings. The bar at the right represents only those emissions from direct combustion of fossil fuels. Because the electricity can be derived from fuels with lower carbon content than current fuels, CO 2 emissions from electricity use in buildings can also be altered on the supply side. Carbon dioxide emissions, including through the use of electricity in buildings, grew from 1971 to 2004 at an annual rate of 2%, about equal to the overall growth rate Gt CO 2 all energy sources emissions from electricity use and district heating in buildings Figure 6.1: Carbon dioxide emissions from energy, 2004 Sources: IEA, 2006e and Price et al direct combustion in buildings 4 This counts all forms of energy use in buildings, including electricity. 391

6 Residential and commercial buildings Chapter 6 of CO 2 emissions from all uses of energy. CO 2 emissions for commercial buildings grew at 2.5% per year and at 1.7% per year for residential buildings during this period. The largest regional increases in CO 2 emissions (including through the use of electricity) for commercial buildings were from developing Asia (30%), North America (29%) and OECD Pacific (18%). The largest regional increase in CO 2 emissions for residential buildings was from Developing Asia accounting for 42% and Middle East/North Africa with 19%. During the past seven years since the IPCC Third Assessment Report (TAR, IPCC, 2001), CO 2 emissions (including through the use of electricity) in residential buildings have increased at a much slower rate than the 30-year trend (annual rate of 0.1% versus trend of 1.4%) and emissions associated with commercial buildings have grown at a faster rate (3.0% per year in last five years) than the 30-year trend (2.2%) (Price et al., 2006). Non-CO 2 emissions (largely halocarbons, CFCs, and HCFCs, covered under the Montreal Protocol and HFCs) from cooling and refrigeration contribute more than 15% of the 8.6 GtCO 2 emissions associated with buildings. About 1.5 GtCO 2 -eq of halocarbon (HFCs, CFCs and HCFCs) emissions, or 60% of the total halocarbon emissions was due to refrigerants and blowing agents for use in buildings (refrigerators, air conditioners and insulation) in Emissions due to these uses are projected to remain about constant until 2015 and decline if effective policies are pursued (IPCC/TEAP, 2005). 6.3 Scenarios of carbon emissions resulting from energy use in buildings Figure 6.2 shows the results for the buildings sector of disaggregating two of the emissions scenarios produced for the IPCC Special Report on Emissions Scenarios (SRES) (IPCC, 2000), Scenarios A1B and B2, into ten world regions (Price et al., 2006). These scenarios show a range of projected buildings related CO 2 emissions (including through the use of electricity): from 8.6 GtCO 2 emissions in 2004 to 11.4 and 15.6 GtCO 2 emissions in 2030 (B2 and A1B respectively), representing an approximately 30% share of total CO 2 emissions in both scenarios. In Scenario B2, which has lower economic growth, especially in 2 Western Europe Central and Eastern Europe Middle East & North Africa 2 EECCA Non-Annex I South Asia 4 Non-Annex I East Asia 2 4 North America Sub Saharan Africa Latin America World Pacific OECD Western Europe Middle East & North Africa 2 Central & Eastern Europe EECCA Non-Annex I East Asia 2 4 North America Sub Saharan Africa Non-Annex I South Asia Pacific OECD World Latin America Figure 6.2: CO 2 emissions including through the use of electricity: A1B (top) and B2 (bottom) IPCC (SRES) scenarios Note: Dark red historic emissions based on Price et al. (2006) modifications of IEA data. Light red projections data based on Price et al. (2006) disaggregation of SRES data; data adjusted to actual 2000 carbon dioxide emissions. EECCA = Countries of Eastern Europe, the Caucasus and Central Asia. 392

7 Chapter 6 Residential and commercial buildings the developing world (except China), two regions account for the largest portion of increased CO 2 emissions from 2004 to 2030: North America and Developing Asia. In Scenario A1B (which shows rapid economic growth, especially in developing nations), all of the increase in CO 2 emissions occurs in the developing world: Developing Asia, Middle East/North Africa, Latin America and sub-saharan Africa, in that order. Overall, average annual CO 2 emissions growth is 1.5% in Scenario B2 and 2.4% in Scenario A1B over the 26-year period. For the purpose of estimating the CO 2 mitigation potential in buildings, a baseline was derived based on the review of several studies. This baseline represents an aggregation of national and regional baselines reported in the studies (see Box 6.1). The building sector baseline derived and used in this chapter shows emissions between the B2 and A1B (SRES) scenarios, with 11.1 Gt of CO 2 -eq emissions in 2020 and 14.3 Gt in 2030 (including electricity emissions). 6.4 GHG mitigation options in buildings and equipment There is an extensive array of technologies that can be used to abate GHG emissions in new and existing residential and commercial buildings. Prior to discussing options for reducing specific end-uses of energy in buildings it is useful to present an overview of energy end-uses in the residential and commercial sectors, where such information is available and to review some principles of energy-efficient design and operation that are broadly applicable. Figure 6.3 presents a breakdown of energy end-use in the residential and commercial sector for the United States and China. The single largest user of energy in residential buildings in both regions is space heating, followed by water heating (China) and other uses primarily electric appliances (USA). The order of the next largest uses are reversed in China and the United States, suggesting that electric appliances will increase in use over time in China. The end-uses in commercial buildings are much less similar between China and the United States. For China, heating is by far the largest end-use. For the United States, the largest end-use is other (plug loads involving office equipment and small appliances). Water heating is the second end-use in China; it is not significant in commercial buildings in the United States. Lighting and cooling are similarly important as the third and fourth largest user in both countries. The single largest use of energy in residential buildings in both regions is for space heating, followed by water heating. Space heating is also the single largest use of energy in commercial 44% other uses U.S. commercial building energy use % space heating 10% space cooling 7% water heating 2% cooking China commercial building energy use % lighting and other 22% water heating 45% space heating 4% refrigeration 21% lighting 14% space cooling U.S. residential building energy use 2005 China residential building energy use % other uses 27% other uses 29% space heating 21% appliances 32% space heating 8% refrigeration 11% space cooling 11% lighting 3% cooking 11% water heating 9% lighting 27% water heating 7% cooking Figure 6.3: Breakdown of residential and commercial sector energy use in United States (2005) and China (2000). Sources: EIA, 2006 and Zhou,

8 Residential and commercial buildings Chapter 6 buildings in the EU, accounting for up to 2/3 of total energy use and is undoubtedly dominant in the cold regions of China and in the Former Soviet Union. Lighting is sometimes the largest single use of electricity in commercial buildings, although in hot climates, air conditioning tends to be the single largest use of electricity Overview of energy efficiency principles Design strategies for energy-efficient buildings include reducing loads, selecting systems that make the most effective use of ambient energy sources and heat sinks and using efficient equipment and effective control strategies. An integrated design approach is required to ensure that the architectural elements and the engineering systems work effectively together Reduce heating, cooling and lighting loads A simple strategy for reducing heating and cooling loads is to isolate the building from the environment by using high levels of insulation, optimizing the glazing area and minimizing the infiltration of outside air. This approach is most appropriate for cold, overcast climates. A more effective strategy in most other climates is to use the building envelope as a filter, selectively accepting or rejecting solar radiation and outside air, depending on the need for heating, cooling, ventilation and lighting at that time and using the heat capacity of the building structure to shift thermal loads on a time scale of hours to days Utilize active solar energy and other environmental heat sources and sinks Active solar energy systems can provide electricity generation, hot water and space conditioning. The ground, ground water, aquifers and open bodies of water, and less so air, can be used selectively as heat sources or sinks, either directly or by using heat pumps. Space cooling methods that dissipate heat directly to natural heat sinks without the use of refrigeration cycles (evaporative cooling, radiative cooling to the night sky, earth-pipe cooling) can be used Increase efficiency of appliances, heating and cooling equipment and ventilation The efficiency of equipment in buildings continues to increase in most industrialized and many developing countries, as it has over the past quarter-century. Increasing the efficiency and where possible reducing the number and size of appliances, lighting and other equipment within conditioned spaces reduces energy consumption directly and also reduces cooling loads but increases heating loads, although usually by lesser amounts and possibly for different fuel types Implement commissioning and improve operations and maintenance The actual performance of a building depends as much on the quality of construction as on the quality of the design itself. Building commissioning is a quality control process that includes design review, functional testing of energy-consuming systems and components, and clear documentation for the owner and operators. Actual building energy performance also depends critically on how well the building is operated and maintained. Continuous performance monitoring, automated diagnostics and improved operator training are complementary approaches to improving the operation of commercial buildings in particular Change behaviour The energy use of a building also depends on the behaviour and decisions of occupants and owners. Classic studies at Princeton University showed energy use variations of more than a factor of two between houses that were identical but had different occupants (Socolow, 1978). Levermore (1985) found a variation of 40% gas consumption and 54% electricity consumption in nine identical children s homes in a small area of London. When those in charge of the homes knew that their consumption was being monitored, the electricity consumption fell. Behaviour of the occupants of non-residential buildings also has a substantial impact on energy use, especially when the lighting, heating and ventilation are controlled manually (Ueno et al., 2006) Utilize system approaches to building design Evaluation of the opportunities to reduce energy use in buildings can be done at the level of individual energy-using devices or at the level of building systems (including building energy management systems and human behaviour). Energy efficiency strategies focused on individual energy-using devices or design features are often limited to incremental improvements. Examining the building as an entire system can lead to entirely different design solutions. This can result in new buildings that use much less energy but are no more expensive than conventional buildings. The systems approach in turn requires an integrated design process (IDP), in which the building performance is optimized through an iterative process that involves all members of the design team from the beginning. The steps in the most basic IDP for a commercial building include (i) selecting a highperformance envelope and highly efficient equipment, properly sized; (ii) incorporating a building energy management system that optimises the equipment operation and human behaviour, and (iii) fully commissioning and maintaining the equipment (Todesco, 2004). These steps alone can usually achieve energy savings in the order of 35 50% for a new commercial building, compared to standard practice, while utilization of more 394

9 Chapter 6 Residential and commercial buildings advanced or less conventional approaches has often achieved savings in the order of 50 80% (Harvey, 2006) Consider building form, orientation and related attributes At the early design stages, key decisions usually made by the architect can greatly influence the subsequent opportunities to reduce building energy use. These include building form, orientation, self-shading, height-to-floor-area ratio and decisions affecting the opportunities for and effectiveness of passive ventilation and cooling. Many elements of traditional building designs in both developed and developing countries have been effective in reducing heating and cooling loads. Urban design, including the clustering of buildings and mixing of different building types within a given area greatly affect the opportunities for and cost of district heating and cooling systems (Section 6.4.7) as well as transport energy demand and the shares of different transport modes (Chapter 5, Section 5.5.1) Minimize halocarbon emissions Many building components notably air conditioning and refrigeration systems, foam products used for insulation and other purposes and fire protection systems may emit greenhouse gases with relatively high global-warming potentials. These chemicals include chlorofluorocarbons, hydrochlorofluorocarbons, halons (bromine-containing fluorocarbons) and hydrofluorocarbons (HFCs). While the consumption of the first three is being eliminated through the Montreal Protocol and various national and regional regulations, their on-going emission is still the subject of strategies discussed in the IPCC special report (IPCC/TEAP, 2005). Meanwhile, the use and emissions of HFCs, mostly as replacements for the three ozone-depleting substances, are increasing worldwide. For many air conditioning and refrigeration applications, the CO 2 emitted during the generation of electricity to power the equipment will typically vastly outweigh the equivalent emissions of the HFC refrigerant. Some exceptions to this general rule exist and two building-related emission sources CFC chillers and HFC supermarket refrigeration systems are discussed further. In addition to these applications, some emission mitigation from air conditioning and refrigeration systems is achievable through easy, low-cost options including education and training, proper design and installation, refrigerant leakage monitoring and responsible use and handling of refrigerants throughout the equipment lifecycle. Like air conditioning and refrigeration systems, most foams and fire protection systems are designed to exhibit low leak rates, and therefore often only emit small portions of the total fluorocarbon under normal use conditions. Upon decommissioning of the building and removal and/or destruction of foam products and fire protection systems, however, large portions of the remaining fluorocarbon content may be released, particularly if no specific measures are adopted to prevent such release. This raises the need to ensure that proper end-of-life management protocols are followed to avoid these unnecessary emissions Thermal envelope The term thermal envelope refers to the shell of the building as a barrier to unwanted heat or mass transfer between the interior of the building and the outside conditions. The effectiveness of the thermal envelope depends on (i) the insulation levels in the walls, ceiling and ground or basement floor, including factors such as moisture condensation and thermal bridges that affect insulation performance; (ii) the thermal properties of windows and doors; and (iii) the rate of exchange of inside and outside air, which in turn depends on the air-tightness of the envelope and driving forces such as wind, inside-outside temperature differences and air pressure differences due to mechanical ventilation systems or warm/cool air distribution. Improvements in the thermal envelope can reduce heating requirements by a factor of two to four compared to standard practice, at a few percent of the total cost of residential buildings, and at little to no net incremental cost in commercial buildings when downsizing of heating and cooling systems is accounted for (Demirbilek et al., 2000; Hamada et al., 2003; Hastings, 2004). A number of advanced houses have been built in various cold-climate countries around the world that use as little as 10% of the heating energy of houses built according to the local national building code (Badescu and Sicre, 2003; Hamada et al., 2003; Hastings, 2004). Reducing the envelope and air exchange heat loss by a factor of two reduces the heating requirement by more than a factor of two because of solar gains and internal heat gains from equipment, occupants and lighting. In countries with mild winters but still requiring heating (including many developing countries), modest (and therefore less costly) amounts of insulation can readily reduce heating requirements by a factor of two or more, as well as substantially reducing indoor summer temperatures, thereby improving comfort (in the absence of air conditioning) or reducing summer cooling energy use (Taylor et al., 2000; Florides et al., 2002; Safarzadeh and Bahadori, 2005) Insulation The choice of insulation material needs to maximize longterm thermal performance of the building element overall. As mentioned previously, this involves consideration of remaining thermal bridges and any water ingress, or other factor, which could result in deterioration of performance over time. For existing buildings, space may be at a premium and the most efficient insulation materials may be needed to minimize thicknesses required. Where upgrading of existing elements is essentially voluntary, minimization of cost and disturbance is equally important and a range of post-applied technologies can 395

10 Residential and commercial buildings Chapter 6 be considered, including cavity wall insulation, spray foams and rolled loft insulation. Only a few specific applications with effective control of end-of life emissions have been identified in which foams containing high GWP blowing agents will lead to lower overall climate impacts than hydrocarbon or CO 2 solutions. However, where this is the case, care should still be taken to optimize life-cycle management techniques in order to minimize blowing agent emissions (see ) Windows The thermal performance of windows has improved greatly through the use of multiple glazing layers, low-conductivity gases (argon in particular) between glazing layers, lowemissivity coatings on one or more glazing surfaces and use of framing materials (such as extruded fibreglass) with very low conductivity. Operable (openable) windows are available with heat flows that have only 25 35% of the heat loss of standard non-coated double-glazed (15 to 20% of singleglazed) windows. Glazing that reflects or absorbs a large fraction of the incident solar radiation reduces solar heat gain by up to 75%, thus reducing cooling loads. In spite of these technical improvements, the costs of glazing and windows has remained constant or even dropped in real terms (Jakob and Madlener, 2004). A major U.S. Department of Energy program is developing electrochromic and gasochromic windows which can dynamically respond to heating and cooling in different seasons Air leakage In cold climates, uncontrolled exchange of air between the inside and outside of a building can be responsible for up to half of the total heat loss. In hot-humid climates, air leakage can be a significant source of indoor humidity. In residential construction, installation in walls of a continuous impermeable barrier, combined with other measures such as weatherstripping, can reduce rates of air leakage by a factor of five to ten compared to standard practice in most jurisdictions in North America, Europe and the cold-climate regions of Asia (Harvey, 2006). In addition to leakage through the building envelope, recent research in the United States has demonstrated that leaks in ducts for distributing air for heating and cooling can increase heating and cooling energy requirements by 20 40% (Sherman and Jump, 1997; O Neal et al., 2002; Francisco et al., 2004). A technology in early commercial use in the United States seals leaks by spraying fine particles into ducts. The sticky particles collect at leakage sites and seal them permanently. This technology is cost-effective for many residential and commercial buildings; it achieves lower costs by avoiding the labour needed to replace or manually repair leaky ducts Heating systems Passive solar heating Passive solar heating can involve extensive sun-facing glazing, various wall- or roof-mounted solar air collectors, double-façade wall construction, airflow windows, thermally massive walls behind glazing and preheating or pre-cooling of ventilation air through buried pipes. Technical details concerning conventional and more advanced passive solar heating techniques, real-world examples and data on energy savings are provided in books by Hastings (1994), Hestnes et al. (2003) and Hastings (2004). Aggressive envelope measures combined with optimisation of passive solar heating opportunities, as exemplified by the European Passive House Standard, have achieved reductions in purchased heating energy by factors of five to thirty (i.e., achieving heating levels less than 15 kwh/ m 2 /yr even in moderately cold climates, compared to 220 and kwh/m 2 /yr for the average of existing buildings in Germany and Central/Eastern Europe, respectively (Krapmeier and Drössler, 2001; Gauzin-Müller, 2002; Kostengünstige Passivhäuser als europäische Standards, 2005) Space heating systems In the industrialized nations and in urban areas in developing countries (in cold winter climates), heating is generally provided by a district heating system or by an onsite furnace or boiler. In rural areas of developing countries, heating (when provided at all) is generally from direct burning of biomass. The following sections discuss opportunities to increase energy efficiency in these systems. Heating systems used primarily in industrialized countries Multi-unit residences and many single-family residences (especially in Europe) use boilers, which produce steam or hot water that is circulated, generally through radiators. Annual Fuel Utilization Efficiencies (AFUE) values range from 80% to 99% for the boiler, not including distribution losses. Modern residential forced-air furnaces, which are used primarily in North America, have AFUE values ranging from 78% to 97% (again, not including distribution system losses). Old equipment tends to have an efficiency in the range of 60 70%, so new equipment can provide substantial savings (GAMA (Gas Appliance Manufacturers Association), 2005). In both boilers and furnaces, efficiencies greater than about 88% require condensing operation, in which some of the water vapour in the exhaust is condensed in a separate heat exchanger. Condensing boilers are increasingly used in Western Europe due to regulation of new buildings, which require higher-efficiency systems. Hydronic systems (in which water rather than air is circulated), especially floor radiant heating systems, are capable of greater energy efficiency than forced air systems because of the low energy required to distribute a given amount of heat, low distribution heat losses and absence of induced infiltration of 396

11 Chapter 6 Residential and commercial buildings outside air into the house due to poorly balanced air distribution systems (low-temperature systems also make it possible to use low-grade solar thermal energy). Heat pumps use an energy input (almost always electricity) to transfer heat from a cold medium (the outside air or ground in the winter) to a warmer medium (the warm air or hot water used to distribute heat in a building). During hot weather, the heat pump can operate in reverse, thereby cooling the indoor space. In winter, drawing heat from a relatively warm source (such as the ground rather than the outside air) and distributing the heat at the lowest possible temperature can dramatically improve the heat pump efficiency. Use of the ground rather than the outside air as a heat source reduced measured energy use for heating by 50 to 60% in two US studies (Shonder et al., 2000; Johnson, 2002). Due to the large energy losses (typically 60 65%) in generating electricity from fossil fuels, heat pumps are particularly advantageous for heating when they replace electric-resistance heating, but may not be preferable to direct use of fuels for heating. The ground can also serve as a lowtemperature heat sink in summer, increasing the efficiency of air conditioning. Coal and biomass burning stoves in rural areas of developing countries Worldwide, about three billion people use solid fuels biomass and, mainly in China, coal in household stoves to meet their cooking, water heating and space heating needs. Most of these people live in rural areas with little or no access to commercial sources of fuel or electricity (WEC (World Energy Council and Food and Agriculture Organization), 1999). Statistical information on fuel use in cooking stoves is sketchy, so any estimates of energy use and associated GHG emissions are uncertain. 5 The global total for traditional biofuel use a good proxy for energy use in household stoves was about 32 EJ in 2002, compared to commercial energy use worldwide of 401 EJ (IEA, 2004c). Worldwide, most household stoves use simple designs and local materials that are inefficient, highly polluting and contribute to the overuse of local resources. Studies of China and India have found that if only the Kyoto Protocol basket of GHGs is considered, biomass stoves appear to have lower emission factors than fossil-fuel alternatives (Smith et al., 2000; Edwards et al., 2004). If products of incomplete combustion (PICs) other than methane and N 2 O are considered, however, then biomass stove-fuel combinations exhibit GHG emissions three to ten times higher than fossil-fuel alternatives, and in many cases even higher emissions than from stoves burning coal briquettes (Goldemberg et al., 2000). Additional heating effects arise from black carbon emissions associated with woodburning stoves. Programmes to develop and disseminate moreefficient biomass stoves have been very effective in China, less so in India and other countries (Barnes et al., 1994; Goldemberg et al., 2000; Sinton et al., 2004). In the long term, stoves that use biogas or biomass-derived liquid fuels offer the greatest potential for significantly reducing the GHG (and black carbon) emissions associated with household use of biomass fuels Cooling and cooling loads Cooling energy can be reduced by: 1) reducing the cooling load on a building, 2) using passive techniques to meet some or all of the load, and 3) improving the efficiency of cooling equipment and thermal distribution systems Reducing the cooling load Reducing the cooling load depends on the building shape and orientation, the choice of building materials and a whole host of other decisions that are made in the early design stage by the architect and are highly sensitive to climate. In general, recently constructed buildings are no longer adapted to prevailing climate; the same building forms and designs are now seen in Stockholm, New York, Houston, Hong Kong, Singapore and Kuwait. However, the principles of design to reduce cooling load for any climate are well known. In most climates, they include: (i) orienting a building to minimize the wall area facing east or west; (ii) clustering buildings to provide some degree of self shading (as in many traditional communities in hot climates); (iii) using high-reflectivity building materials; (iv) increasing insulation; (v) providing fixed or adjustable shading; (vi) using selective glazing on windows with a low solar heat gain and a high daylight transmission factor and avoiding excessive window area (particularly on east- and west-facing walls); and (vii) utilizing thermal mass to minimize daytime interior temperature peaks. As well, internal heat loads from appliances and lighting can be reduced through the use of efficient equipment and controls. Increasing the solar reflectivity of roofs and horizontal or near-horizontal surfaces around buildings and planting shade trees can yield dramatic energy savings. The benefits of trees arise both from direct shading and from cooling the ambient air. Rosenfeld et al. (1998) computed that a very large-scale, citywide program of increasing roof and road albedo and planting trees in Los Angeles could yield a total savings in residential cooling energy of 50 60%, with a 24 33% reduction in peak air conditioning loads Passive and low-energy cooling techniques Purely passive cooling techniques require no mechanical energy input, but can often be greatly enhanced through small amounts of energy to power fans or pumps. A detailed discussion of passive and low-energy cooling techniques can be found in 5 Estimates are available for China and India, collectively home to about one third of the world s population. Residential use of solid fuels in China, nearly all used in stoves, was about 9 EJ in 2002, or 18% of all energy use in the country (National Bureau of Statistics, 2004). The corresponding figures for India were 8 EJ and 36% (IEA, 2004c). In both cases, nearly all of this energy is in the form of biomass. 397

12 Residential and commercial buildings Chapter 6 Harvey (2006) and Levermore (2000). Highlights are presented below: Natural and night-time ventilation Natural ventilation reduces the need for mechanical cooling by: directly removing warm air when the incoming air is cooler than the outgoing air, reducing the perceived temperature due to the cooling effect of air motion, providing night-time cooling of exposed thermal mass and increasing the acceptable temperature through psychological adaptation when the occupants have control of operable windows. When the outdoor temperature is 30 C, the average preferred temperature in naturally ventilated buildings is 27 C, compared to 25 C in mechanically ventilated buildings (de Dear and Brager, 2002). Natural ventilation requires a driving force and an adequate number of openings, to produce airflow. Natural ventilation can be induced through pressure differences arising from insideoutside temperature differences or from wind. Design features, both traditional and modern, that create thermal driving forces and/or utilize wind effects include courtyards, atria, wind towers, solar chimneys and operable windows (Holford and Hunt, 2003). In addition to being increasingly employed in commercial buildings in Europe, natural ventilation is starting to be used in multi-story commercial buildings in more temperate climates in North America (McConahey et al., 2002). Natural ventilation can be supplemented with mechanical ventilation as needed. In climates with a minimum diurnal temperature variation of 5 C to 7 C, natural or mechanically assisted night-time ventilation, in combination with exposed thermal mass, can be very effective in reducing daily temperature peaks and, in some cases, eliminating the need for cooling altogether. Simulations carried out in California indicate that night-time ventilation is sufficient to prevent peak indoor temperatures from exceeding 26 C over 43% of California in houses with an improved envelope and modestly greater thermal mass compared to standard practice (Springer et al., 2000). For Beijing, da Graça et al. (2002) found that thermally and wind-driven night-time ventilation could eliminate the need for air conditioning of a six-unit apartment building during most of the summer if the high risk of condensation during the day due to moist outdoor air coming into contact with the night-cooled indoor surfaces could be reduced. Evaporative cooling There are two methods of evaporatively cooling the air supplied to buildings. In a direct evaporative cooler, water evaporates directly into the air stream to be cooled. In an indirect evaporative cooler, water evaporates into and cools a secondary air stream, which cools the supply air through a heat exchanger without adding moisture. By appropriately combining direct and indirect systems, evaporative cooling can provide comfortable conditions most of the time in most parts of the world. Subject to availability of water, direct evaporative cooling can be used in arid areas; indirect evaporative cooling extends the region of applicability to somewhat more humid climates. A new indirect-direct evaporative cooler in the development phase indicated savings in annual cooling energy use of 92 to 95% for residences and 89 to 91% for a modular school classroom in simulations for a variety of California climate zones (DEG, 2004). Other passive cooling techniques Underground earth-pipe cooling consists of cooling ventilation air by drawing outside air through a buried air duct. Good performance depends on the climate having a substantial annual temperature range. Desiccant dehumidification and cooling involves using a material (desiccant) that removes moisture from air and is regenerated using heat. Solid desiccants are a commercially available technology. The energy used for dehumidification can be reduced by 30 to 50% compared to a conventional overcooling/reheat scheme (50 to 75% savings of conventional sources if solar energy is used to regenerate the desiccant) (Fischer et al., 2002; Niu et al., 2002). In hot-humid climates, desiccant systems can be combined with indirect evaporative cooling, providing an alternative to refrigerationbased air conditioning systems (Belding and Delmas, 1997) Air conditioners and vapour-compression chillers Air conditioners used for houses, apartments and small commercial buildings have a nominal COP (cooling power divided by fan and compressor power, a direct measure of efficiency) ranging from 2.2 to 3.8 in North America and Europe, depending on operating conditions. More efficient mini-split systems are available in Japan, ranging from 4.5 to 6.2 COP for a 2.8 kw cooling capacity unit. Chillers are larger cooling devices that produce chilled water (rather than cooled air) for use in larger commercial buildings. COP generally increases with size, with the largest and most efficient centrifugal chillers having a COP of up to 7.9 under full-load operation and even higher under part-load operation. Although additional energy is used in chiller-based systems for ventilation, circulating chilled water and operating a cooling tower, significant energy savings are possible through the choice of the most efficient cooling equipment in combination with efficient auxiliary systems (see Section for principles). Air conditioners from small room-sized units to large building chillers generally employ a halocarbon refrigerant in a vapour-compression cycle. Although the units are designed to exhibit low refrigerant emission rates, leaks do occur and additional emissions associated with the installation, service and disposal of this equipment can be significant. The emissions will vary widely from one installation to the next and depend greatly on the practices employed at the site. In some cases, the GWPweighted lifetime emissions of the refrigerant will outweigh the CO 2 emissions associated with the electricity, highlighting the need to consider refrigerant type and handling as well as energy 398

13 Chapter 6 Residential and commercial buildings efficiency when making decisions on the purchase, operation, maintenance and replacement of these systems. Until recently, the penetration of air conditioning in developing countries has been relatively low, typically only used in large office buildings, hotels and high-income homes. That is quickly changing however, with individual apartment and home air conditioning becoming more common in developing countries, reaching even greater levels in developed countries. This is evident in the production trends of typical room-tohouse sized units, which increased 26% (35.8 to 45.4 million units) from 1998 to 2001 (IPCC/TEAP, 2005) Heating, ventilation and air conditioning (HVAC) systems The term HVAC is generally used in reference to commercial buildings. HVAC systems include filtration and, where required by the climate, humidification and dehumidification as well as heating and cooling. However, energy-efficient houses in climates with seasonal heating are almost airtight, so mechanical ventilation has to be provided (during seasons when windows will be closed), often in combination with the heating and/or cooling system, as in commercial buildings Principles of energy-efficient HVAC design In the simplest HVAC systems, heating or cooling is provided by circulating a fixed amount of air at a sufficiently warm or cold temperature to maintain the desired room temperature. The rate at which air is circulated in this case is normally much greater than that needed for ventilation to remove contaminants. During the cooling season, the air is supplied at the coldest temperature needed in any zone and reheated as necessary just before entering other zones. There are a number of changes in the design of HVAC systems that can achieve dramatic savings in the energy use for heating, cooling and ventilation. These include (i) using variable-air volume systems so as to minimize simultaneous heating and cooling of air; (ii) using heat exchangers to recover heat or coldness from ventilation exhaust air; (iii) minimizing fan and pump energy consumption by controlling rotation speed; (iv) separating the ventilation from the heating and cooling functions by using chilled or hot water for temperature control and circulating only the volume of air needed for ventilation; (v) separating cooling from dehumidification functions through the use of desiccant dehumidification; (vi) implementing a demand-controlled ventilation system in which ventilation airflow changes with changing building occupancy which alone can save 20 to 30% of total HVAC energy use (Brandemuehl and Braun, 1999); (vii) correctly sizing all components; and (viii) allowing the temperature maintained by the HVAC system to vary seasonally with outdoor conditions (a large body of evidence indicates that the temperature and humidity set-points commonly encountered in air-conditioned buildings are significantly lower than necessary (de Dear and Brager, 1998; Fountain et al., 1999), while computer simulations by Jaboyedoff et al. (2004) and by Jakob et al. (2006) indicate that increasing the thermostat by 2 C to 4 C will reduce annual cooling energy use by more than a factor of three for a typical office building in Zurich, and by a factor of two to three if the thermostat setting is increased from 23 C to 27 C for night-time air conditioning of bedrooms in apartments in Hong Kong (Lin and Deng, 2004). Additional savings can be obtained in mixed-mode buildings, in which natural ventilation is used whenever possible, making use of the extended comfort range associated with operable windows, and mechanical cooling is used only when necessary during periods of very warm weather or high building occupancy Alternative HVAC systems in commercial buildings The following paragraphs describe two alternatives to conventional HVAC systems in commercial buildings that together can reduce the HVAC system energy use by 30 to 75%. These savings are in addition to the savings arising from reducing heating and cooling loads. Radiant chilled-ceiling cooling A room may be cooled by chilling a large fraction of the ceiling by circulating water through pipes or lightweight panels. Chilled ceiling (CC) cooling has been used in Europe since at least the mid-1970s. In Germany during the 1990s, 10% of retrofitted buildings used CC cooling (Behne, 1999). Significant energy savings arise because of the greater effectiveness of water than air in transporting heat and because the chilled water is supplied at 16 C to 20 C rather than at 5 C to 7 C. This allows a higher chiller COP when the chiller operates, but also allows more frequent use of water-side free cooling, in which the chiller is bypassed altogether and water from the cooling tower is used directly for space cooling. For example, a cooling tower alone could directly meet the cooling requirements 97% of the time in Dublin, Ireland and 67% of the time in Milan, Italy if the chilled water is supplied at 18 C (Costelloe and Finn, 2003). Displacement ventilation Conventional ventilation relies on turbulent mixing to dilute room air with ventilation air. A superior system is displacement ventilation (DV) in which air is introduced at low speed through many diffusers in the floor or along the sides of a room and is warmed by internal heat sources (occupants, lights, plug-in equipment) as it rises to the top of the room, displacing the air already present. The thermodynamic advantage of displacement ventilation is that the supply air temperature is significantly higher for the same comfort conditions (about 18 o C compared with about 13 o C in a conventional mixing ventilation system). It also permits significantly smaller airflow. DV was first applied in northern Europe; by 1989 it had captured 50% of the Scandinavian market for new industrial buildings and 25% for new office buildings (Zhivov and 399

14 Residential and commercial buildings Chapter 6 Rymkevich, 1998). The building industry in North America has been much slower to adopt DV; by the end of the 1990s fewer than 5% of new buildings used under-floor air distribution systems (Lehrer and Bauman, 2003). Overall, DV can reduce energy use for cooling and ventilation by 30 to 60%, depending on the climate (Bourassa et al., 2002; Howe et al., 2003) Building energy management systems (BEMS) BEMSs are control systems for individual buildings or groups of buildings that use computers and distributed microprocessors for monitoring, data storage and communication (Levermore, 2000). The BEMS can be centrally located and communicate over telephone or Internet links with remote buildings having outstations so that one energy manager can manage many buildings remotely. With energy meters and temperature, occupancy and lighting sensors connected to a BEMS, faults can be detected manually or using automated fault detection software (Katipamula et al., 1999), which helps avoid energy waste (Burch et al., 1990). With the advent of inexpensive, wireless sensors and advances in information technology, extensive monitoring via the Internet is possible. Estimates of BEMS energy savings vary considerably: up to 27% (Birtles and John, 1984); between 5% and 40% (Hyvarinen, 1991; Brandemuehl and Bradford, 1999; Brandemuehl and Braun, 1999; Levermore, 2000); up to 20% in space heating energy consumption and 10% for lighting and ventilation; and 5% to 20% overall (Roth et al., 2005) Commissioning Proper commissioning of the energy systems in a commercial building is a key to efficient operation (Koran, 1994; Kjellman et al., 1996; IEA, 2005; Roth et al., 2005). Building commissioning is a quality control process that begins with the early stages of design. Commissioning helps ensure that the design intent is clear and readily tested, that installation is subjected to onsite inspection and that all systems are tested and functioning properly before the building is accepted. A systems manual is prepared to document the owner s requirements, the design intent (including as-built drawings), equipment performance specifications and control sequences. Recent results of building commissioning in the USA showed energy savings of up to 38% in cooling and/or 62% in heating and an average higher than 30% (Claridge et al., 2003). A study by Mills et al. (2005) reviewed data from 224 US buildings that had been commissioned or retro-commissioned. The study found that the costs of commissioning new buildings were typically outweighed by construction cost savings due to fewer change orders and that retro-commissioning produced median energy savings of 15% with a median payback period of 8.5 months. It is very difficult to assess the energy benefits of commissioning new buildings due to the lack of a baseline Operation, maintenance and performance benchmarking Once a building has been commissioned, there is a need to maintain its operating efficiency. A variety of methods to monitor and evaluate performance and diagnose problems are currently under development (Brambley et al., 2005). Postoccupancy evaluation (POE) is a useful complement to ongoing monitoring of equipment and is also useful for ensuring that the building operates efficiently. A UK study of recently constructed buildings found that the use of POE identified widespread energy wastage (Bordass et al., 2001a; Bordass et al., 2001b). Cogeneration and District Heating/Cooling Buildings are usually part of a larger community. If the heating, cooling and electricity needs of a larger collection of buildings can be linked together in an integrated system without major distribution losses, then significant savings in primary energy use are possible beyond what can be achieved by optimising the design of a single building. Community-scale energy systems also offer significant new opportunities for the use of renewable energy. Key elements of an integrated system can include: 1) district heating networks for the collection of waste or surplus heat and solar thermal energy from dispersed sources and its delivery to where it is needed; 2) district cooling networks for the delivery of chilled water for cooling individual buildings; 3) central production of steam and/or hot water in combination with the generation of electricity (cogeneration) and central production of cold water; 4) production of electricity through photovoltaic panels mounted on or integrated into the building fabric; 5) diurnal storage of heat and coldness produced during off-peak hours or using excess wind-generated electricity; and 6) seasonal underground storage of summer heat and winter coldness. District heating (DH) is widely used in regions with large fractions of multi-family buildings, providing as much as 60% of heating and hot water energy needs for 70% of the families in Eastern European countries and Russia (OECD/IEA, 2004). While district heating can have major environmental benefits over other sources of heat, including lower specific GHG emissions, systems in these countries suffer from the legacies of past mismanagement and are often obsolete, inefficient and expensive to operate (Lampietti and Meyer, 2003, Ürge- Vorsatz et al., 2006). Making DH more efficient could save 350 million tonnes of CO 2 emissions in these countries annually, accompanied by significant social, economic and political benefits (OECD/IEA, 2004). The greatest potential improvement in the efficiency of district heating systems is to convert them to cogeneration systems that involve the simultaneous production of electricity and useful heat. For cogeneration to provide an improvement in efficiency, a use has to be found for the waste heat. Centralized production of heat in a district heat system can be more efficient than onsite boilers or furnaces even in the absence of cogeneration 400

15 Chapter 6 Residential and commercial buildings and in spite of distribution losses, if a district-heating network is used with heat pumps to upgrade and distribute heat from scattered sources. Examples include waste heat from sewage in Tokyo (Yoshikawa, 1997) and Gothenberg, Sweden (Balmér, 1997) and low-grade geothermal heat in Tianjin, China, that is left over after higher-temperature heat has been used for heating and hot water purposes (Zhao et al., 2003). Waste heat from incineration has been used, particularly in northern Europe. Chilled water supplied to a district-cooling network can be produced through trigeneration (the simultaneous production of electricity, heat and chilled water), or it can be produced through a centralized chilling plant independent of power generation. District cooling provides an alternative to separate chillers and cooling towers in multi-unit residential buildings that would otherwise use inefficient small air conditioners. In spite of the added costs of pipes and heat exchangers in district heating and cooling networks, the total capital cost can be less than the total cost of heating and cooling units in individual buildings, (Harvey, 2006, Chapter 15). Adequate control systems are critical to the energy-efficient operation of both district cooling and central (building-level) cooling systems. District heating and cooling systems, especially when combined with some form of thermal energy storage, make it more economically and technically feasible to use renewable sources of energy for heating and cooling. Solar-assisted district heating systems with storage can be designed such that solar energy provides 30 to 95% of total annual heating and hot water requirements under German conditions (Lindenberger et al., 2000). Sweden has been able to switch a large fraction of its building heating energy requirements to biomass energy (plantation forestry) for its district heating systems (Swedish Energy Agency, 2004) Active collection and transformation of solar energy Buildings can serve as collectors and transformers of solar energy, meeting a large fraction of their energy needs on a sustainable basis with minimal reliance on connection to energy grids, although for some climates this may only apply during the summer. As previously discussed, solar energy can be used for daylighting, for passive heating and as one of the driving forces for natural ventilation, which can often provide much or all of the required cooling. By combining a high-performance thermal envelope with efficient systems and devices, 50 75% of the heating and cooling energy needs of buildings as constructed under normal practice can either be eliminated or satisfied through passive solar design. Electricity loads, especially in commercial buildings, can be drastically reduced to a level that allows building-integrated photovoltaic panels (BiPV) to meet much of the remaining electrical demand during daytime hours. Photovoltaic panels can be supplemented by other forms of active solar energy, such as solar thermal collectors for hot water, space heating, absorption space cooling and dehumidification Building-integrated PV (BiPV) The principles governing photovoltaic (PV) power generation and the prospects for centralized PV production of electricity are discussed in Chapter 4, Section Building-integrated PV (BiPV) consists of PV modules that function as part of the building envelope (curtain walls, roof panels or shingles, shading devices, skylights). BiPV systems are sometimes installed in new showcase buildings even before the systems are generally cost-effective. These early applications will increase the rate at which the cost of BiPVs comes down and the technical performance improves. A recent report presents data on the cost of PV modules and the installed-cost of PV systems in IEA countries (IEA, 2003b). Electricity costs from BiPV at present are in the range of US$/kWh in good locations, but can drop considerably with mass production of PV modules (Payne et al., 2001). Gutschner et al. (2001) have estimated the potential for power production from BiPV in IEA member countries. Estimates of the percentage of present total national electricity demand that could be provided by BiPV range from about 15% (Japan) to almost 60% (USA) Solar thermal energy for heating and hot water Most solar thermal collectors used in buildings are either flat-plate or evacuated-tube collectors. 6 Integrated PV/thermal collectors (in which the PV panel serves as the outer part of a thermal solar collector) are also commercially available (Bazilian et al., 2001; IEA, 2002). Combisystems are solar systems that provide both space and water heating. Depending on the size of panels and storage tanks, and the building thermal envelope performance, 10 to 60% of the combined hot water and heating demand can be met by solar thermal systems at central and northern European locations. Costs of solar heat have been /kwh for large domestic hot water systems and /kwh for combisystems with diurnal storage (Peuser et al., 2002). Worldwide, over 132 million m 2 of solar collector surface for space heating and hot water were in place by the end of China accounts for almost 40% of the total (51.4 million m 2 ), followed by Japan (12.7 million m 2 ) and Turkey (9.5 million m 2 ) (Weiss et al., 2005). 6 See Peuser et al. (2002) and Andén (2003) for technical information. 401

16 Residential and commercial buildings Chapter Domestic hot water Options to reduce fossil or electrical energy used to produce hot water include (i) use of water saving fixtures, more waterefficient washing machines, cold-water washing and (if used at all) more water-efficient dishwashers (50% typical savings); (ii) use of more efficient and better insulated water heaters or integrated space and hot-water heaters (10 20% savings); (iii) use of tankless (condensing or non-condensing) water heaters, located close to the points of use, to eliminate standby and greatly reduce distribution heat losses (up to 30% savings, depending on the magnitude of standby and distribution losses with centralized tanks); (v) recovery of heat from warm waste water; (vi) use of air-source or exhaust-air heat pumps; and (vii) use of solar thermal water heaters (providing 50 90% of annual hot-water needs, depending on climate). The integrated effect of all of these measures can frequently reach a 90% savings. Heat pumps using CO 2 as a working fluid are an attractive alternative to electric-resistance hot water heaters, with a COP of up to (Saikawa et al., 2001; Yanagihara, 2006) Lighting systems Lighting energy use can be reduced by 75 to 90% compared to conventional practice through (i) use of daylighting with occupancy and daylight sensors to dim and switch off electric lighting; (ii) use of the most efficient lighting devices available; and (iii) use of such measures as ambient/task lighting High efficiency electric lighting Presently 1.9 GtCO 2 are emitted by electric lighting worldwide, equivalent to 70% of the emissions from light passenger vehicles (IEA, 2006b). Continuous improvements in the efficacy 7 of electric lighting devices have occurred during the past decades and can be expected to continue. Advances in lamps have been accompanied by improvements in occupancy sensors and reductions in cost (Garg and Bansal, 2000; McCowan et al., 2002). A reduction in residential lighting energy use of a factor of four to five can be achieved compared to incandescent/halogen lighting. For lighting systems providing ambient (general space) lighting in commercial buildings, the energy required can be reduced by 50% or more compared to old fluorescent systems through use of efficient lamps (ballasts and reflectors, occupancy sensors, individual or zone switches on lights and lighter colour finishes and furnishings. A further 40 to 80% of the remaining energy use can be saved in perimeter zones through daylighting (Rubinstein and Johnson, 1998; Bodart and Herde, 2002). A simple strategy to further reduce energy use is to provide a relatively low background lighting level, with local levels of greater illumination at individual workstations. This strategy is referred to as task/ambient lighting and is popular in Europe. Not only can this alone cut lighting energy use in half, but it provides a greater degree of individual control over personal lighting levels and can reduce uncomfortable levels of glare and high contrast. About one third of the world s population depends on fuel-based lighting (such as kerosene, paraffin or diesel), contributing to the major health burden from indoor air pollution in developing countries. While these devices provide only 1% of global lighting, they are responsible for 20% of the lighting-related CO 2 emissions and consume 3% of the world s oil supply. A CFL or LED is about 1000 times more efficient than a kerosene lamp (Mills, 2005). Efforts are underway to promote replacement of kerosene lamps with LEDs in India. Recent advances in light-emitting diode (LED) technology have significantly improved the cost-effectiveness, longevity and overall viability of stand-alone PV-powered task lighting (IEA, 2006b) Daylighting Daylighting systems involve the use of natural lighting for the perimeter areas of a building. Such systems have light sensors and actuators to control artificial lighting. Opportunities for daylighting are strongly influenced by architectural decisions early in the design process, such as building form; the provision of inner atria, skylights and clerestories (glazed vertical steps in the roof); and the size, shape and position of windows. IEA (2000) provides a comprehensive sourcebook of conventional and less conventional techniques and technologies for daylighting. A number of recent studies indicate savings in lighting energy use of 40 to 80% in the daylighted perimeter zones of office buildings (Rubinstein and Johnson, 1998; Jennings et al., 2000; Bodart and Herde, 2002; Reinhart, 2002; Atif and Galasiu, 2003; Li and Lam, 2003). The management of solar heat gain along with daylighting to reduce electric lighting also leads to a reduction in cooling loads. Lee et al. (1998) measured savings for an automated Venetian blind system integrated with office lighting controls, finding that lighting energy savings averaged 35% in winter and ranged from 40 to 75% in summer. Monitored reductions in summer cooling loads were 5 to 25% for a southeast-facing office in Oakland, California building, with even larger reductions in peak cooling loads. Ullah and Lefebvre (2000) reported measured savings of 13 to 32% for cooling plus ventilation energy using automatic blinds in a building in Singapore. An impediment to more widespread use of daylighting is the linear, sequential nature of the design process. Based on a survey of 18 lighting professionals in the USA, Turnbull 7 This is the ratio of light output in lumens to input power in watts. 402

17 Chapter 6 Residential and commercial buildings and Loisos (2000) found that, rather than involving lighting consultants from the very beginning, architects typically make a number of irreversible decisions at an early stage of the design that adversely impact daylighting, then pass on their work to the lighting consultants and electrical engineers to do the lighting design. As a result, the lighting system becomes, de facto, strictly an electrical design Household appliances, consumer electronics and office equipment Energy use by household appliances, office equipment and consumer electronics, from now on referred to as appliances, is an important fraction of total electricity use in both households and workplaces (Kawamoto et al., 2001; Roth et al., 2002). This equipment is more than 40% of total residential primary energy demand in 11 large OECD nations 8 (IEA, 2004f). The largest growth in electricity demand has been in miscellaneous equipment (home electronics, entertainment, communications, office equipment and small kitchen equipment), which has been evident in all industrialized countries since the early 1980s. Such miscellaneous equipment now accounts for 70% of all residential appliance electricity use in the 11 large OECD nations (IEA, 2004f). Appliances in some developing countries constitute a smaller fraction of residential energy demand. However, the rapid increase in their saturation in many dynamically developing countries such as China, especially in urban areas, demonstrates the expected rise in importance of appliances in the developing world as economies grow (Lawrence Berkeley National Laboratory, 2004). On a primary energy basis appliances undoubtedly represent a larger portion of total energy use for residential than for commercial buildings. In the United States, for example, they account for almost 55% of total energy consumption in commercial buildings. Miscellaneous equipment and lighting combined account for more than half of total energy consumption in commercial buildings in the United States and Japan (Koomey et al., 2001; Murakami et al., 2006). The most efficient appliances require a factor of two to five less energy than the least efficient appliances available today. For example, in the USA, the best horizontal-axis clotheswashing machines use less than half the energy of the best vertical-axis machines (FEMP, 2002), while refrigerator/freezer units meeting the current US standard (478 kwh/yr) require about 25% of the energy used by refrigerator/freezers sold in the USA in the late 1970s (about 1800 kwh/yr) and about 50% of energy used in the late 1980s. Available refrigerator/freezers of standard US size use less than 400 kwh/yr (Brown et al., 1998). However, this is still in excess of the average energy use by (generally smaller) refrigerators in Sweden, the Netherlands, Germany and Italy in the late 1990s (IEA, 2004f). Standby and low power mode use by consumer electronics (i.e., energy used when the machine is turned off) in a typical household in many countries often exceeds the energy used by a refrigerator/freezer unit that meets the latest US standards, that is often more than 500 kwh/yr, (Bertoldi et al., 2002). The growing proliferation of electronic equipment such as set-top boxes for televisions, a wide variety of office equipment (in homes as well as offices) and sundry portable devices with attendant battery chargers combined with inefficient power supplies (Calwell and Reeder, 2002) and highly inefficient circuit designs that draw unnecessary power in the resting or standby modes have caused this equipment to be responsible for a large fraction of the electricity demand growth in both residential and commercial buildings in many nations. Efforts are underway especially at the International Energy Agency and several countries (e.g., Korea, Australia, Japan and China) to reduce standby energy use by a factor of two to three (Ross and Meier, 2002; Fung et al., 2003). Electricity use by office equipment may not yet be large compared to electricity use by the HVAC system, but (as noted) it is growing rapidly and is already an important source of internal heat gain in offices and some other commercial buildings. The biggest savings opportunities are: 1) improved power supply efficiency in both active and low-power modes, 2) redesigned computer chips that reduce electricity use in low-power mode, and 3) repeated reminders to users to turn equipment off during non-working hours. The cooking stove, already referred to in Section for heating, is a major energy-using appliance in developing countries. However, there is particular concern about emissions of products of incomplete combustion described in that section. Two-and-a-half billion people in developing countries depend on biomass, such as wood, dung, charcoal and agricultural residues, to meet their cooking energy needs (IEA, 2006e). Options available to reduce domestic cooking energy needs include: 1) improved efficiency of biomass stoves; 2) improved access to clean cooking fuels, both liquid and gaseous; 3) access to electricity and low-wattage and low-cost appliances for low income households; 4) non-electric options such as solar cookers; 5) efficient gas stoves; and 6) small electric cooking equipment such as microwaves, electric kettles or electric frying pans. Improved biomass stoves can save from 10 to 50% of biomass consumption for the same cooking service (REN21 (Renewable Energy Policy Network), 2005) at the same time reducing indoor air pollution by up to one-half. Although the overall impact on emissions from fuel switching can be either positive or negative, improved modern fuels and greater conversion efficiency would result in emission reductions from all fuels (IEA, 2006e). 8 Australia, Denmark, Finland, France, Germany, Italy, Japan, Norway, Sweden, the United Kingdom, and the United States. 403

18 Residential and commercial buildings Chapter Supermarket refrigeration systems Mitigation options for food-sales and service buildings, especially supermarkets and hypermarkets extend beyond the energy savings mitigation options reviewed so far (e.g., high efficiency electric lighting, daylighting, etc.). Because these buildings often employ large quantities of HFC refrigerants in extensive and often leaky systems, a significant share of total GHG emissions are due to the release of the refrigerant. In all, emissions of the refrigerant can be greater than the emissions due to the system energy use (IPCC/TEAP, 2005). Two basic mitigation options are reviewed in IPCC/TEAP report: leak reduction and alternative system design. Refrigerant leakage rates are estimated to be around 30% of banked system charge. Leakage rates can be reduced by system design for tightness, maintenance procedures for early detection and repairs of leakage, personnel training, system leakage record keeping and end-of-life recovery of refrigerant. Alternative system design involves for example, applying direct systems using alternative refrigerants, better containment, distributed systems, indirect systems or cascade systems. It was found that up to 60% lower LCCP values can be obtained by alternative system design (IPCC/TEAP, 2005) Energy savings through retrofits There is a large stock of existing and inefficient buildings, most of which will still be here in 2025 and even Our long-term ability to reduce energy use depends critically on the extent to which energy use in these buildings can be reduced when they are renovated. The equipment inside a building, such as the furnace or boiler, water heater, appliances, air conditioner (where present) and lighting is completely replaced over time periods ranging from every few years to every years. The building shell walls, roof, windows and doors lasts much longer. There are two opportunities to reduce heating and cooling energy use by improving the building envelope: (i) at any time prior to a major renovation, based on simple measures that pay for themselves through reduced energy costs and potential financial support or incentives; and (ii) when renovations are going to be made for other (non-energy) reasons, including replacement of windows and roofs Conventional retrofits of residential buildings Cost-effective measures that can be undertaken without a major renovation of residential buildings include: sealing points of air leakage around baseboards, electrical outlets and fixtures, plumbing, the clothes dryer vent, door joists and window joists; weather stripping of windows and doors; and adding insulation in attics, to walls or wall cavities. A Canadian study found that the cost-effective energy savings potential ranges from 25 30% for houses built before the 1940s, to about 12% for houses built in the 1990s (Parker et al., 2000). In a carefully documented retrofit of four representative houses in the York region of the UK, installation of new window and wooden door frames, sealing of suspended timber ground floors and repair of cracks in plaster reduced the rate of air leakage by a factor of (Bell and Lowe, 2000). This, combined with improved insulation, doors and windows, reduced the heating energy required by an average of 35%. Bell and Lowe (2000) believe that a reduction of 50% could be achieved at modest cost using well-proven (early 1980s) technologies, with a further 30 40% reduction through additional measures. Studies summarized by Francisco et al. (1998) indicate that air-sealing retrofits alone can save an average of 15 20% of annual heating and air conditioning energy use in US houses. Additional energy savings would arise by insulating pipework and ductwork, particularly in unconditioned spaces. Rosenfeld (1999) refers to an AeroSeal technique (see Sec ) that he estimates is already saving three billion US$/yr in energy costs in the USA. Without proper sealing, homes in the USA lose, on average, about one-quarter of the heating and cooling energy through duct leaks in unconditioned spaces attics, crawl spaces, basements. In a retrofit of 4003 homes in Louisiana, the heating, cooling and water heating systems were replaced with a ground-source heat pump system. Other measures were installation of attic insulation and use of compact fluorescent lighting and water saving showerheads. Space and hot water heating previously provided by natural gas was supplied instead by electricity (through the heat pump), but total electricity use still decreased by one third (Hughes and Shonder, 1998). External Insulation and Finishing Systems (EIFSs) provide an excellent opportunity for upgrading the insulation and improving the air-tightness of single- and multi-unit residential buildings, as well as institutional and commercial buildings. This is because of the wide range of external finishes that can be applied, ranging from stone-like to a finish resembling aged plaster. A German company manufacturing some of the components used in EIFSs undertook a major renovation of some of its own 1930s multi-unit residential buildings. The EIFSs in combination with other measures achieved a factor of eight measured reduction in heating energy use (see de). An envelope upgrade of an apartment block in Switzerland reduced the heating requirement by a factor of two, while replacing an oil-fired boiler at 85% seasonal average efficiency with an electric heat pump having a seasonal average COP of 3.2 led to a further large decrease in energy use. The total primary energy requirement decreased by about 75% (Humm, 2000) Conventional retrofits of institutional and commercial buildings There are numerous published studies showing that energy savings of 50 to 75% can be achieved in commercial buildings through aggressive implementation of integrated 404

19 Chapter 6 Residential and commercial buildings sets of measures. These savings can often be justified in terms of the energy-cost savings alone, although in other cases full justification requires consideration of a variety of less tangible benefits. In the early 1990s, a utility in California sponsored a 10 million US$ demonstration of advanced retrofits. In six of seven retrofit projects, an energy savings of 50% was obtained; in the seventh project, a 45% energy savings was achieved. For Rosenfeld (1999), the most interesting result was not that an alert, motivated team could achieve savings of 50% with conventional technology, but that it was very hard to find a team competent enough to achieve these results. Other, recent examples that are documented in the published literature include: A realized savings of 40% in heating, plus cooling, plus ventilation energy use in a Texas office building through conversion of the ventilation system from one with constant to one with variable air flow (Liu and Claridge, 1999); A realized savings of 40% of heating energy use through the retrofit of an 1865 two-story office building in Athens, where low-energy was achieved through some passive technologies that required the cooperation of the occupants (Balaras, 2001); A realized savings of 74% in cooling energy use in a onestory commercial building in Florida through duct sealing, chiller upgrade and fan controls (Withers and Cummings, 1998); Realized savings of 50 70% in heating energy use through retrofits of schools in Europe and Australia (CADDET, 1997); Realized fan, cooling and heating energy savings of 59, 63 and 90% respectively in buildings at a university in Texas; roughly half due to standard retrofit and half due to adjustment of the control-system settings (which were typical for North America) to optimal settings (Claridge et al., 2001) Solar retrofits of residential, institutional and commercial buildings Solar retrofit performed in Europe under the IEA Solar and Cooling Program achieved savings in space heating of 25 80% (Harvey, 2006, Chapter 14). The retrofit examples described above, while achieving dramatic (35 75%) energy savings, rely on making incremental improvements to the existing building components and systems. More radical measures involve reconfiguring the building so that it can make direct use of solar energy for heating, cooling and ventilation. The now-completed Task 20 of the IEA s Solar Heating and Cooling (SHC) implementing agreement was devoted to solar retrofitting techniques. Solar renovation measures that have been used are installation of roof- or façade-integrated solar air collectors; roof-mounted or integrated solar DHW heating; transpired solar air collectors, advanced glazing of balconies, external transparent insulation; and construction of a second-skin façade over the original façade. Case studies are presented in Boonstra and Thijssen (1997), Haller et al. (1997) and Voss (2000a), Voss (2000b) and are summarized in Harvey (2006), Chapter 14) Trade-offs between embodied energy and operating energy The embodied energy in building materials needs to be considered along with operating energy in order to reduce total lifecycle energy use by buildings. The replacement of materials that require significant amounts of energy to produce (such as concrete and steel) with materials requiring small amounts of energy to produce (such as wood products) will reduce the amount of energy embodied in buildings. Whether this reduces energy use on a lifecycle basis, however, depends on the effect of materials choice on the energy requirements for heating and cooling over the lifetime of the building and whether the materials are recycled at the end of their life (Börjesson and Gustavsson, 2000; Lenzen and Treloar, 2002). For typical standards of building construction, the embodied energy is equivalent to only a few years of operating energy, although there are cases in which the embodied energy can be much higher (Lippke et al., 2004). Thus, over a 50-year time span, reducing the operating energy is normally more important than reducing the embodied energy. However, for traditional buildings in developing countries, the embodied energy can be large compared to the operating energy, as the latter is quite low. In most circumstances, the choice that minimizes operating energy use also minimizes total lifecycle energy use. In some cases, the high embodied energy in high-performance building envelope elements (such as krypton-filled double- or tripleglazed windows) can be largely offset from savings in the embodied energy of heating and/or cooling equipment (Harvey, 2006, Chapter 3), so a truly holistic approach is needed in analysing the lifecycle energy use of buildings Trade-offs involving energy-related emissions and halocarbon emissions Emissions of halocarbons from building cooling and refrigeration equipment, heat pumps and foam insulation amount to 1.5 GtCO 2 -eq at present, compared to 8.6 GtCO 2 from buildings (including through the use of electricity) (IPCC/ TEAP, 2005). Emissions due to these uses are projected only to 2015 and are constant or decline in this period. Halocarbon emissions are thus an important consideration. Issues pertaining to stratospheric ozone and climate are comprehensively reviewed in the recent IPCC/TEAP report (IPCC/TEAP, 2005). Halocarbons (CFCs, HCFCs and HFCs) are involved as a working fluid in refrigeration equipment (refrigerators, freezers and cold storage facilities for food), heating and cooling of buildings (heat pumps, air conditioners and chillers) and as an blowing agent used in foam insulation for refrigerators, pipes 405

20 Residential and commercial buildings Chapter 6 and buildings. All three groups are greenhouse gases. The GWP of HCFCs is generally lower than CFCs. The GWP of HFCs is also generally lower than that of the CFCs, but generally slightly higher than that of the HCFCs. The consumption (production plus imports, minus exports, minus destruction) of CFCs except for critical uses (e.g., medical devices) stopped in 1996 in developed countries, while developing countries have been given to 2010 to eliminate consumption. HCFCs are being phased out, also for reasons of ozone depletion, but will not be completely phased out of production until 2030 in developed countries and 2040 in developing countries. Nevertheless, projected emissions of HCFCs and HFCs (and ongoing emissions from CFC banks) are sufficiently high that scenarios of halocarbon emissions related to buildings in 2015 show almost the same emissions as in 2002 (about 1.5 GtCO 2 - eq. emissions). For the coming decade or longer, the bank of CFCs in the stock of cooling equipment and foams is so large that particular attention needs to be given to recovering these CFCs. Lifetime emissions of refrigerants from cooling equipment, expressed as CO 2 -eq per unit of cooling, have fallen significantly during the past 30 years. Leakage rates are generally in the order of 3%, but rates as high as 10 15% occur. By 2010, it is expected that HFCs will be the only halocarbon refrigerant to be used in air conditioners and heat pumps manufactured in developed countries. Non-halocarbon refrigerants can entail similar efficiency benefits if the heat pump is fully optimised. Thus, both the performance of the heat pump and the impact of halocarbon emissions need to be considered in evaluating the climatic impact of alternative choices for refrigerants. The climatic impact of air conditioners and most chillers is generally dominated by the energy used to power them. For leakage of HFC refrigerants at rates of 1 to 6%/yr (IPCC/TEAP, 2005) (best practice is about 0.5%/yr) and recovery of 85% of the refrigerant (compared to % in typical practice) at the end of a 15-year life, refrigerant leakage accounts for only 1 to 5% of the total impact on climate of the cooling equipment to up to 20%, without end-of-life recovery, of the total impact (derived from (IPCC/TEAP, 2005). This demonstrates the importance of end-of-life recovery, which is highly uncertain for HFCs at present. However, for CFC chillers, the high GWP of the refrigerant and the typical high leakage of older CFCbased designs cause the refrigerant to be a significant factor in overall emissions. This demonstrates that emphasis needs to be put on the replacement of CFC chillers in both developed and developing countries for which hydrocarbons are now widely used in EU countries. that direct refrigerant emissions can drop from 40 60% of the total emissions in a typical system to 15% for improved systems. The value is 0% for systems using hydrocarbon or ammonia refrigerants. Although some designs may incur a slight increase in energy use, total (energy + refrigerant) emissions are nonetheless significantly reduced. For foam insulation blown with halocarbons, the benefit of reduced heating energy use can outweigh the effect of leakage of blowing agent when insulating buildings that were previously either poorly insulated or uninsulated (Ashford et al., 2005). However, for high levels of insulation, the opposite becomes true (Harvey, 2007) without end-of-life recovery of the blowing agent. In general terms, the use of methods such as Life Cycle Climate Performance (LCCP) is essential in evaluating the most appropriate course of action in each situation Summary of mitigation options in buildings The key conclusion of section 6.4 is that substantial reductions in CO 2 emissions from energy use in buildings can be achieved over the coming years using existing, mature technologies for energy efficiency that already exist widely and that have been successfully used (high agreement, much evidence). There is also a broad array of widely accessible and cost-effective technologies and know-how that can abate GHG emissions in buildings to a significant extent that has not as yet been widely adopted. Table 6.1 summarizes selected key technological opportunities in buildings for GHG abatement in five world regions based on three criteria. Twenty-one typical technologies were selected from those described in section 6.4. As economic and climatic conditions in regions largely determine the applicability and importance of technologies, countries were divided into three economic classes and two climatic types. The three criteria include the maturity of the technology, cost/ effectiveness and appropriateness. Appropriateness includes climatic, technological and cultural applicability. For example, direct evaporative cooling is ranked as highly appropriate in dry and warm climates but it is not appropriate in humid and warm climates. The assessment of some technologies depends on other factors, too. For instance, the heat pump system depends on the energy source and whether it is applied to heating or cooling. In these cases, variable evaluation is indicated in the table. The energy/hfc relationship for air conditioners does not hold for most large built-up refrigeration systems, such as those found in supermarkets and hypermarkets. Roughly half of the total equivalent emissions from these systems result from the refrigerant, in case an HFC blend is used. Various designs explored in IPCC/TEAP report (IPCC/TEAP, 2005) indicate 406

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